There has recently been considerable research into organic thin-film light emitting devices which emit light when electrons injected from a cathode and holes injected from an anode recombine within an organic fluorescent body interposed between the cathode and the anode. Such light emitting devices are a focus of attention on account of their characteristics of thin shape, high luminance at a low driving voltage and polychromic light emission based on suitable selection of the fluorescent materials.
Numerous research organizations have been carrying out such research since C. W. Tang and co-workers at Kodak first described the fact that an organic thin-film light emitting device emits light of high luminance. A typical organic thin-film light emitting element construction proposed by the Kodak research group is that in which there are provided, in turn, on an ITO glass substrate, a hole transporting diamine compound, tris (8-hydroxyquinolate)aluminum(III) as the emissive layer and Mg:Ag (alloy) as the cathode. A 1,000 cd/m2 green colored light emission is possible at a driving voltage of about 10 V (refer to Non-Patent Document 1).
It has intensively been studied to apply the organic thin-film light emitting device as a display since various luminescent colors can be obtained by using various luminescence materials in the emissive layer. Research on the use of a green emissive material as a primary-color emissive material is at the most advanced stage and intensive study is being performed so as to improve characteristics of a red emissive material and a blue emissive material.
One of largest problems associated with organic thin-film light emitting devices is to reconcile the luminance efficiency, chromatic purity and durability of the device. In particular, there are few blue emissive materials which provide a device which has excellent chromatic purity and durability and, at the same time, reliability. For example, there is disclosed a technique of using a styrylamine derivative (refer to Patent Document 1), a perylene derivative (refer to Patent Document 2) and an anthracene derivative (refer to Patent Document 3) as a blue guest material. There is also disclosed a technique of using a pyrene compound in a blue light emitting device (refer to Patent Documents 4, 5). There is also reported an example in which a compound (refer to Patent Documents 6 to 8) having a pyrene skeletal structure containing a diarylboryl group introduced therein is used in a light emitting device. However, all of the resultant devices had insufficient chromatic purity and durability.
[Patent Document 1]
Japanese Unexamined Patent Publication (Kokai) No. 5-17765
[Patent Document 2]
Japanese Unexamined Patent Publication (Kokai) No. 2003-86380
[Patent Document 3]
International Publication No. WO 00/40586 Pamphlet
[Patent Document 4]
Japanese Unexamined Patent Publication (Kokai) No. 5-21161
[Patent Document 5]
Japanese Unexamined Patent Publication (Kokai) No. 2001-118682
[Patent Document 6]
Japanese Unexamined Patent Publication (Kokai) No. 2000-294373
[Patent Document 7]
Japanese Unexamined Patent Publication (Kokai) No. 2000-290645
[Patent Document 8]
Kohyo (National Publication of Translated Version) No. 2005-501372
[Non-Patent Document 1]
Applied Physics Letters (USA) 1987, Vol. 51, No. 12, pp. 913-915